Conventional hair bleach powders are compositions which are used for lightening hair color. Typically, these products are sold to the consumer as dry powders, which must be mixed with aqueous solutions of hydrogen peroxide before they are used. Upon mixing, the components in the bleach powder and the hydrogen peroxide solution form an activated bleaching composition which is then applied to the hair. The activated bleaching composition lightens the hair by oxidizing natural hair pigments, such as melanin.
Typical hair bleach powders contain a reactant which interacts with hydrogen peroxide to form oxygen, which breaks down melanin in hair. Commonly, such reactants include, inter alia, peroxygenated ammonium, sodium or potassium salts of persulfates, perborates, percarbonates and the like.
It is usually necessary for adequate oxygen formation to have an activated bleach composition with a pH in the range of 9.5-11.5 upon addition of the hydrogen peroxide solution. The peroxide and the persulfate are both acids, which are activated at a basic pH. Accordingly, it is common to add a base, such as an amine alkali compound or a metasilicate, to hair bleach powders.
Conventional hair bleach powders may also contain other additives including thickeners, such as hydroxyalkylated cellulose, that help form the powder base. Such bleach powders are also susceptible, upon storage, to degradation resulting from atmospheric moisture. Thus, it is also common to add desiccants, such as silica derivatives, to prevent the bleach powders from being degraded by moisture before use.
There are several disadvantages associated with conventional hair bleach powders. Specifically, conventional bleach powders have a tendency to form dust during handling, transport and storage. Dusting also occurs during transfer of the bleach powder to the mixing chamber prior to admixing with the aqueous solution of hydrogen peroxide. Moreover, the persulfates and the alkaline silicate reactants are corrosive, and can be dangerous to the handler. These dusts irritate the eyes, the respiratory canal and the mucous membranes. Ammonium persulfate is an especially problematic irritant.
For these reasons, various attempts have been made to reduce the dusting characteristics of hair bleach powders. Partial success has been achieved through the addition of substantially water insoluble compounds, such as oils or liquid waxes, to the bleach powder. These oils or waxes coat the individual powder particles and agglomerate them into larger sized particles. Such bleach powders are thus rendered substantially dust-free due to their lack of small particles.
Published European Patent Application Publication No. 0583,767 A2, ("EP '767"), provides an example of this approach. EP '767 discloses a dry free flowing, dust free hair bleach powder, wherein a powder base comprising ammonium, sodium and potassium persulfate salts is treated with "inert adsorbates" or inert liquids which include, inter alia, mineral oils, natural oils and fluorosilicone fluids.
These inert liquid additives, which are oils, are disclosed as performing two functions: (1) as an adhesive to aggregate small powder particles into particles having a size greater than 40.mu. and (2) as a lubricant to coat the particles so they do not abrade and form dust. Therefore, the inert liquid additives function primarily as de-dusting agents.
In order to obtain the desired characteristics of the compositions taught by EP '767, the inert liquid is said to comprise about 10-25% by weight of the hair bleach powder with the preferred range being about 14-20% by weight.
U.S. Pat. No. 4,170,637 ("'637 patent") also recites a hair bleach composition which comprises an intimate mixture of particulate persulfate salts and alkaline silicates dispersed in a hydrophobic organic carrier, such as an oil or wax, present in an amount from about 30-70% by weight of the total mixture. The resulting compositions are not powders, but have a "paste to cream" consistency.
European Patent Publication No. 0,560,088 B1 ("EP '088") discloses dust free bleach powders that are also treated with oils and/or liquid waxes. These ingredients comprise from 2.5 to 25%, and preferably between 8 and 12%, of the total weight of the bleach powder. The added substances are also taught as being substantially water-insoluble ("Industrie et technologie des Corps Gras" (Industry and Technology of Fatty Substances), Alton E. Bayley; "Romps Chemie Lexicon", Oho Albrecht and Neumuller; "Introduction to Fats and Oils Technology", Peter J. Wan; Larousse Dictionary). Specifically, EP '088 recites the use of paraffin oil and silicone oil, which are hydrophobic, water insoluble substances.
While the above-recited treatments produce substantially dust-free bleach powders, these powders still suffer from significant drawbacks, because they form unstable oil based emulsions upon mixture with the aqueous hydrogen peroxide. Therefore, to compensate for this instability, additional components, such as surfactants and emulsifiers (e.g., polyoxyethylenestearates or polypropyleneoxides), must be added to the powder. Moreover, when bleach powders containing oil-based de-dusting agents are mixed with aqueous hydrogen peroxide, they take a long time to form a usable paste.
Another undesirable aspect of conventional bleaching compositions is that they fail to exhibit satisfactory thixotropy characteristics. An activated bleaching composition with good thixotropy moves through the hair with little effort, but also remains in the location where it is applied. In other words, good thixotropy properties help the bleach composition recover from sheer forces exerted on it during application to hair. Activated bleaching compositions prepared with the above-mentioned prior art dust-free hair bleach powders do not exhibit good thixotropy, but instead require excessive embrocation or wetting to effectively and evenly bleach the hair. It is difficult to obtain desired thixotropy for an activated bleaching composition, since a moderately low viscosity is required to impart the right amount of spreadability. However, if the viscosity is too low, the prepared bleach paste or cream will not stay in its applied location. Therefore, it is critical for an activated bleaching composition to have an optimum viscosity to impart desirable aesthetic characteristics to the hair.
Conventional bleach powders have further disadvantages in that they decompose under humid conditions and have relatively low ignition temperatures. Moreover, none of the conventional dust-free bleaching powders incorporates substantially hydrophilic de-dusting agents, which simultaneously suppress formation of dust and impart improved thixotropy characteristics to activated bleaching compositions made from these powders.